Exemplary embodiments of the present invention relate to a method for fabricating a semiconductor device, and more particularly, to a method for fabricating carbon hard mask for a semiconductor device.
In general, a semiconductor device includes a variety of active elements and passive elements. The active elements and the passive elements are implemented by patterns disposed on a substrate. Therefore, a process of forming patterns is essential in a process of fabricating a semiconductor device. In order to form patterns on a substrate, a mask pattern is formed on a pattern target layer, and an etching process is performed using the mask pattern as an etching barrier layer. A photoresist layer has been widely used as the mask pattern. However, as the integration density of the device increases, it is necessary to form the photoresist layer thinly in order to form fine patterns. A variety of materials are used for the pattern target layer. In recent years, the use of a hard mask layer having a rigid characteristic has increased.
Examples of materials used in the hard mask layer include silicon oxynitride (SiON), silicon nitride (Si3N4), and carbon (C). Among these materials, a carbon hard mask layer has an advantage in that it has selectivity to most pattern target layers because it is etched by oxygen (O2). Thus, the application of the carbon hard mask layer has rapidly expanded. The use of the carbon hard mask layer in the formation of patterns is disclosed in U.S. Pat. Nos. 5,378,316 and 5,656,128. According to these documents, the carbon hard mask layer is deposited by a plasma enhanced chemical vapor deposition (PECVD) process.
In the case of using the PECVD process to deposit the carbon hard mask layer, the card hard mask layer is deposited using CxHy, e.g., C3H6 or C2H2, as source gas within a PECVD chamber at a temperature of about 300-550° C. and RF power of 1,500-2,000 W. Under those conditions, the deposited carbon hard mask layer has hydrogen bonding, where the amount of the hydrogen bonding may be changed according to the temperature. As one example, at a temperature of about 300° C., there is about 40% hydrogen in the carbon hard mask layer. When the carbon hard mask layer is deposited at a temperature of 550° C., there is about 20% hydrogen. It is known that hydrogen bonding is very unstable. Accordingly, a subsequent thermal treatment can remove hydrogen from the carbon hard mask layer, or hydrogen may be removed by having it react with an etching solution or an etching gas in a subsequent etching process.
FIG. 1 is a graph showing a pressure variation with respect to a temperature change of a chamber where a plurality of samples each having a carbon hard mask layer formed by a PECVD process are loaded. As illustrated in FIG. 1, when a thermal treatment is performed at a predetermined temperature, for example, about 600° C. or more, as indicated by “A the pressure inside the chamber rapidly increased. Specifically, the pressure inside the chamber is increased by H or CH from the carbon hard mask layer when a hydrogen bonding within the carbon hard mask layer is broken by a high-temperature thermal treatment.
As such, when hydrogen comes out of the carbon hard mask layer in an H type or a C—H bonded type, it is accumulated at an interface between the carbon hard mask layer and a layer above the carbon hard mask layer. The accumulated H or C—H lowers adsorption force between the carbon hard mask layer and the layer disposed above the carbon hard mask layer by a subsequent etching process or thermal treatment. As a result, the layer disposed above the carbon hard mask layer may be lifted from the carbon hard mask layer.